The significance of this project relates to the need for a high resolution SPECT (Single Photon Emission Computed Tomography) imaging system to perform functional brain imaging in both academic centers and hospitals. For many disease, processes involving disturbances in brain functions. SPECT imaging has been shown to provide diagnostic information which is similar to that obtained from PET (Positron Emission Tomography) studies but which is not available from other anatomically oriented imaging techniques such as CT and MRI. It seems that PET technology is staying mainly in major medical centers, while SPECT is to be the more wide-spread clinical technique for non-invasive functional imaging. The long term objective is to develop a new type of SPECT scanner to fulfill the commercial and clinical need for high performance brain imaging with the new radiopharmaceuticals in a cost-effective manner. The specific aims in the Phase I proposal are focused on the development of multi-crystal detector modules. Two different modules are proposed. Preliminary simulation studies have shown promising results. Detailed procedures are defined to evaluate the technical merit and feasibility of this modular approach to complement the design of a cylindrical SPECT system being developed in our lab. The commercial market for a dedicated high performance brain SPECT scanner is booming and promises to be very substantial. Our optimistic outlook of the commercial viability of the projected end system is based on the high resolution of the collimator and low cost of the cylindrical detector system. The expected sensitivity of the system is 4 times of that of a conventional single head rotating camera SPECT system designed for the same spatial resolution specifications.